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Matsuyama A.,National Institute for Minamata Disease | Eguchi T.,National Institute for Minamata Disease | Sonoda I.,National Institute for Minamata Disease | Tada A.,Nagasaki University | And 5 more authors.
Water, Air, and Soil Pollution | Year: 2011

The speciation of mercury (Hg) in Minamata Bay (Japan) was studied over a 2-year period (2006-2008). Concentrations of dissolved total Hg, dissolved methylmercury (MeHg), particulate total Hg, and suspended solids were 0.43±0.14 ng/l (mean±standard deviation), 0.10±0.06 ng/l, 3.04±2.96 ng/l, and 5.94± 2.10 mg/l, respectively. Correlations between concentrations of particulate total Hg and suspended solids at four depths (surface: 0 m; mid-depth: -6 m,-10 m; and bottom +1 m layer) were only significant in the bottom +1 m layer. The mean dissolved MeHg concentration and the ratio of dissolved MeHg to dissolved total Hg were considerably higher in summer compared to other seasons. The data suggest that bottom sediment was not the sole source of MeHg, and that MeHg may be produced in the water column by the conversion of divalent Hg eluted from resuspended bottom sediment. The correlation between seawater characteristics such as salinity, temperature, dissolved oxygen (DO), and dissolved MeHg concentration indicates that Hg methylation could be influenced by the heterotrophic activity of microorganisms in the seawater. In particular, inverse correlations were observed between DO, salinity, and MeHg concentration. However, dissolved MeHg concentrations did not correlate with seawater characteristics such as pH or chlorophyll-a. © Springer Science+Business Media B.V. 2010.

Tomiyasu T.,Kagoshima University | Takenaka S.,Kagoshima University | Noguchi Y.,Kagoshima University | Kodamatani H.,Kagoshima University | And 5 more authors.
Marine Chemistry | Year: 2014

To estimate the current contamination levels in Minamata Bay, the vertical and horizontal distributions of mercury in the sediment were investigated. Sediment core samples were collected in 2002, 2006, 2008, and 2010 at 12 locations by gravity core sampling in Minamata Bay and Fukuro Bay, which is located in the southern part of Minamata Bay. The average total mercury concentrations during each year in the surface sediment were 2.47-3.34 and 3.50-4.66mgkg-1 for Minamata Bay and Fukuro Bay, respectively; significant variation in the values was not observed during the study period. The total mercury concentration in Fukuro Bay increased with increasing depth and reached a maximum at 8-14cm from the surface and decreased with increasing depth in the deeper layer. In Minamata Bay, the total mercury concentration did not change significantly from the surface to a depth of 10cm and the values were considerably higher than the background level. In the lower layers of the long cores taken from both areas, the total mercury concentration decreased with depth, and the deepest layers exhibited relatively uniform low values. These values can be considered to represent the background concentration in the absence of anthropogenic influence. The depth of the sediment affected by the effluent was estimated to be 20±7cm and 33±4cm for Minamata Bay and Fukuro Bay, respectively. Furthermore, it was estimated from the average concentration and volume of the contaminated layer that approximately 1ton of discharged mercury remained in the sediment of the two bays. © 2014 Elsevier B.V.

Akito M.,Japan Institute for Environmental Sciences | Shinichiro Y.,Kyushu University | Akihiro H.,Kyushu University | Michiaki K.,Japan Institute for Environmental Sciences | And 3 more authors.
Marine Pollution Bulletin | Year: 2014

A detailed investigation of mercury concentrations in the bottom sediments of Minamata Bay was performed in May, 2012. A total of 691 sediment samples were obtained from 107 sampling points in the bay. The weighted average total mercury concentration and the total mass of mercury in the bottom sediments of Minamata Bay were estimated to be 2.3. mg/kg dry weight basis and 3.4. tons, respectively. The average concentration of total mercury in the surface layer of the sediments was 3.0. mg/kg dry weight basis, and the distribution pattern of total mercury concentrations in the surface layer was found to have changed little in comparison to results reported 25. years ago. In addition, based on the results of seawater monitoring in Minamata Bay from 2010 to 2012, the amounts of total mercury and methylmercury mobilized from sediments and dissolved in the water column were 0.7 and 0.1. kg/yr, respectively. © 2014 Elsevier Ltd.

Matsuyama A.,Japan Institute for Environmental Sciences | Yano S.,Kyushu University | Hisano A.,Kyushu University | Kindaichi M.,Japan Institute for Environmental Sciences | And 4 more authors.
Marine Pollution Bulletin | Year: 2016

This study was carried out to evaluate the present-day chemical properties of methylmercury in surface sediment in Minamata Bay where a dredging project was completed 28. years ago. Present-day sediment from Minamata Bay consists of sandy silt, and the average loss-on-ignition in surface sediment was 7.0. ±. 2.3%. The average methylmercury concentrations in the upper sediment layers were significantly higher than those in the lower sediment layers. Currently, the concentrations in sediments in Minamata Bay do not exceed the Japanese regulatory standard value for mercury. The average concentration of methylmercury in Minamata Bay surface sediment was 1.74. ±. 1.0. ng/g on a dry weight basis (n = 107). The methylmercury concentration in Minamata Bay surface sediment was almost 16 times higher than that in surface sediment from Isahaya Bay surface sediment, which was 0.11. ±. 0.045. ng/g on a dry weight basis (n = 5). © 2016.

Iwai-Shimada M.,Tohoku University | Iwai-Shimada M.,Japan Society for the Promotion of Science | Satoh H.,Tohoku University | Nakai K.,Tohoku University | And 3 more authors.
Chemosphere | Year: 2015

The human fetus is known to be exposed to methylmercury (MeHg), but little is known about the risk of infant exposure via breast milk. To evaluate the lactational exposure to MeHg via breast milk in Japanese infants, the levels of total mercury (THg) and MeHg were determined in breast milk and maternal blood using samples from a birth cohort study at the Tohoku Study of Child Development. Maternal blood and breast milk were collected one day postpartum and one month after delivery, respectively. The median THg (and MeHg) concentrations in maternal RBCs, plasma and breast milk were 17.8ngg-1 (17.8ngg-1), 1.51ngg-1 (1.33ngg-1) and 0.81ngg-1 (0.45ngg-1), respectively (n=27). The median percentage of MeHg in THg was 54% in breast milk. Breast milk contained substantial amounts of MeHg, which was strongly associated with the internal accumulation of MeHg and the lipid content of the milk (r=0.684). The range of lipid contents in milk varied widely from 0.50 to 6.60g/100g of milk, with a median of 3.60g/100g. The median (range) weekly average intake of MeHg via breast milk was estimated to be 0.63μgkg-1 (0.08-1.68μgkg-1) BW/week. Because the MeHg and lipid contents in milk substantially fluctuate, an investigation of the variations of MeHg and lipid content in breast milk may be required for a more precise risk assessment. © 2015 Elsevier Ltd.

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